Vacuum circuit breaker

ABSTRACT

A vacuum circuit breaker in which a lid which hermetically and movably supports through a bellows a holder of a movable electrode disposed opposite to a fixed electrode is electrically connected with a terminal for said movable electrode in such a manner as to lead from said lid to said terminal through said connection a current which otherwise might flow in shunt with an arc, in metal shields through the electrode metal melted by the arcing heat during a breaking operation, said metal shields being provided for preventing the conduction of a vacuum cylinder made of insulating material to contain said electrodes, said current in shunt with an arc being thereby prevented from flowing through said bellows.

United States Patent [1 1 Saito July 17, 1973 VACUUM CIRCUIT BREAKER[75] Inventor: Osamu Saito, Hitachi, Japan [73] Assignee: Hitachi, Ltd.,Tokyo, Japan [22] Filed: Aug. 28, 1970 [211 App]. No.: 67,874

[30] Foreign Application Priority Data Sept. 3, i969 Japan 44/69349 [52]US. Cl. 200/144 B, 200/50 A [51] Int. Cl. H0lh 33/66 [58] Field ofSearch 200/144 B, 50 A [56] References Cited UNITED STATES PATENTS3,555,223 1/1971 Robinson et a1. 200/144 B 3,123,698 3/1964 Waterton200/144 B 3,189,715 6/1965 Jennings 200/144 B FOREIGN PATENTS ORAPPLICATIONS 2/1965 France ZOO/144.2

Primary ExaminerRobert S. Macon AttorneyCraig, Antonelli and Hill [57]ABSTRACT A vacuum circuit breaker in which a lid which hermetically andmovably supports through a bellows a holder of a movable electrodedisposed opposite to a fixed electrode is electrically connected with aterminal for said movable electrode in such a manner as to lead fromsaid lid to said terminal through said connection a current whichotherwise might flow in shunt with an arc, in metal shields through theelectrode metal melted by the arcing heat during a breaking operation,said metal shields being provided for preventing the conduction of avacuum cylinder made of insulating material to contain said electrodes,said current in shunt with an are being thereby prevented from flowingthrough said bellows.

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SHEEI 2 UP 2 INVENTOR OSRMu smTo ATTORNEYS The present invention relatesto a vacuum circuit breaker with an improved current path for a movableelectrode.

With a fixed and a movable electrode each supported by an electrodeholder in a highly vacuumized cylinder madeof an insulating material, avacuum circuit breaker is so constructed that there is a bellows connecting between the holder of the movable electrode and an upper lid ofthe cylinder, which bellows maintains the highly vacuumized conditioninside the cylinder, the movable electrode being movable by a certaindistance with respect to the fixed electrode. In addition, a metalshield is provided around the electrodes to prevent a metal component ofthe electrodes melted by the are heat at the time of current breakingfrom being attached on the surface of the cylinder and thuscontaminating the insulating material thereof. In the aboveconstruction, the vacuum circuit breaker proper is supported by a tankmade of insulating material through a lower lid, an upper lid onlysupporting the movable electrode holder so as not to be deviated fromthe center position, so that the force required to contact theelectrodes for conducting a large current and the force to detach themfrom each other is transmitted from an outside control device throughthe electrode holders and the electrodes to the lower lid which supportsthe fixed electrode, thereby preventing the me chanical force from beingapplied to the weak cylinder.

In breaking a large current, a hole or puncture sometimes develops inthe bellows, impairing the function of the vacuum circuit breaker.Seeking the cause of such a hole or puncture, the inventor has foundthat at the time of breaking a large current a great quantity of metalvapor from the surface of the electrodes fills not only the spacebetween the electrodes but also the neighborhood of the lids of theinner cylinder and around the bellows. Also, since the electric field isconcentrated near around the ends of the metal shield, an electricdischarge occurs between the lids and the metal shield, causing a partof the current to flow in parallel with the breaking current to theterminal for themovable electrodethrough the bellows.

After an experiment, the inventor found that when a current of 25 KA(7.2 KV) is broken the branch current flowing through the bellows-reaches as high as several thousands ampere and stays at that level forabout one-fourth of a cycle. The bellows wall is usually as thick as 0.1mm to maintain the high vacuum inside and it is supposed that the branchcurrent flowing through the bellows causes the wall to be heated,melting a part of it to develop a hole.

An object of the present invention is to provide an improved vacuumcircuit breaker in which said branch current is prevented from flowingthrough the bellows.

Another object of the present invention is to provide a reliable vacuumcircuit breaker with a long useful life, equipped with a strong bellowswhich'are not damaged by the branch current.

A third object of the present invention is to provide a vacuum circuitbreaker in which no current flows from the holder for the movableelectrode to the terminal thereof, the sole function of the holder ofthe movable electrode being to guide the same.

Still another object of the present invention is to provide a smallervacuum circuit breaker which has a high resistance against a creepingdischarge along the cylinder and is adapted to be used for ahigh'voltage circuit.

Still another object of the present invention is to provide ahigh-voltage vacuum circuit breaker with greater safety to an operator.

The feature of the present invention is that the upper lid of themovable electrode is electrically connected with the terminal of themovable electrode, to which is led the branch current which flowsthrough the metal vapor diffused from the electrodes and the metalshields at the time of the current breaking, thereby to reduce to almostzero the current in the bellows.

The above and other objects, features and advantages will be madeapparent by the detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. I shows a cross-sectional view of the vacuum circuit breakeraccording to the present invention;

FIG. 2 shows a cross-sectional view of an embodiment of the presentinvention.

Referring to FIG. 1, the reference numeral 1 shows the whole structureof the vacuum circuit breaker. The vacuum chamber 7 consists of acylinder 2 made of an insulating material such as ceramics and an uppermetal lid 5 and a lower metal lid 6 which are fastened on both ends ofsaid cylinder by means of the fasteners 3 and 4. In the vacuum chamberare the movable electrode 8 and the fixed electrode 11, the former beingmounted for movement through the upper lid 5 by means of the holder 9and the bellows 10 and the latter being fixed on the lower lid 6 throughthe holder 12.

The vacuum chamber 7 is vacuumized to the extent of 10 mmHg or less atthe time of current breaking the electrodes 8 and 11 are detached fromeach other by moving the holder 9 in the direction shown by the arrow,thereby causing an are between the electrodes which is extinguished bythe high capability of the vacuum for insulation and are extinguishing.

While the arc is generated, the surface of the electrodes is melted bythe arcing heat and the metal vapor is diffused in the vacuum, attachingitself on the inside surface of the cylinder 2 with the result that saidinside surface of the cylinder 2 is less insulated. To prevent this, themetal shield 13 disposed on the cylinder 2 surrounds the electrodes 8and 11 with the additional metal shields l4 and 15 being placed on theupper and lower lids. The shields serve as a barrier between thecylinder 2 and the electrodes gap in order to prevent the metal vaporfrom advancing directly towards the wall of the cylinder 2. On the lowerlid 6 is a stud 16 which, together with the supporting plate 17, fastensthe vacuum circuit breaker proper to the flange 18a of the tank 18. Theholder 12 for the fixed electrode 11 is mounted on the outside terminalplate 19 from which a current flows to the fixed electrode 11. The stud20 on the upper lid 5 is elastically held by the guide 22 for the holder9 through the spring 21, the guide 22 being fixed on the flange 18b ofthe tank 18 through the supporting plate 24 and the foot 23. The guide22, the foot 23 and the supporting plate 24 are made of a metal andintegrated with each other, the guide 22 being electrically connectedwith the upper lid 5 through the lead wire 25. The holder 9 of themovable electrode is provided with a collector 26 which together with anupper outside terminal plate 27 is fixed on the supporting plate 24 bymeans of an appropriate fastening means including a bolt, etc., therebyelectrically connecting the holder 9 with the upper outside terminalplate 27. To prevent a short-circuit between the holder 9 and the guide22., the insulating material 29 is inserted therebetween.

When an arc is generated during a breaking opera tion, the electricfield is concentrated between the metal shields l3 and 14 and betweenthe metal shields 13 and 15. The dielectric strength at theabovementioned portions markedly drops due to the diffusion of meltedmetal caused by the arcing heat especially when a large current is cutoff, so that electricity is discharged between the metal shields l3 and14 and between the metal shields 13 and 15 through the metal vapor orbetween the fixed electrode 11 and the metal shield 13. As a result, apart of the current flows through the above-mentioned branch circuit inshunt with the are between the electrodes. Since the resistance of thebellows is far greater than that of the lead wire 25, this undesirablebranch current flow to the outside terminal plate 27 not through thebellows 10 but through the lead wire 25. After that, according as thearc current is reduced near zero, the metal is melted at a lower rateand the density in the vacuum chamber 7 is reduced as the diffused metalis deposited on the surface of the metal shields 13, 14 and 15,resulting in less branch current. The insulation between the electrodes8 and 11 is thus restored as a result of the disappearance of the arebetween the electrodes.

FIG. 2 illustrates the vacuum circuit breaker according to the presentinvention installed on a carrier in order to incorporate it into anenclosed switchboard. A floor plate 30 is closely attached on the bottomof the tank 18, which is also provided with hermetical bushings 31 and32. An insulating material such as silicon oil or SF gas is contained inthe space between the cylinder 2 and the tank 18 to improve the creepingresistance of the outer surface of the cylinder 2. The heat generated atthe collector portions or junction points by the Joule effect isabsorbed by the insulating material and is carried away by convectionthrough the material. Thus, the insulating material contributes to, theprevention of an excessiverise in the temperature at such collectorportions or junction points. The tank 18 and the bushings 31 and 32 arecovered with a grounded metal film on their outer surfaces to protect anoperator from an electric shock the metal film being arranged so as notto contact the portions of the circuit breaker having a potentialapplied thereto in the manner known in the art.

The floor plate is directly or indirectly fixed on the carrier 33 whichis movable in the horizontal direction by means of the wheels 34a and34b, whereby the bushings 31 and 32 is connected with or disconnectedfrom bus bars, etc. (not shown in the drawing) located opposite to eachother. The holder 9 for the movable electrode is operated by theoperating mechanism in the carrier 33 through the link mechanismpartially shown by the numeral 35.

As can be seen from above, the vacuum circuit breaker of the presentinvention has such an advantage that the current to be cut off does notflow through the bellows during the breaking operation, so that Jouleheat generated by the current does not damage the be]- lows.Consequently, the reliability of the vacuum circuit breaker is improvedand the useful life thereof is lengthened.

Instead of the connection of the upper lid 5 and the guide 22 throughthe lead wire 25 as employed in the above-mentioned embodiment, aconnection of, say, the holder 9 or the collector 26 and the upper lid 5can achieve the sameeffect.

What is claimed is:

l. A vacuum circuit breaker comprising at least a pair of electrodesrelatively detachable from each other disposed in a vacuum chamber madeairtight by a surrounding cylinder of insulating material and an upperand lower metal lid attached on both ends thereof, said vacuum chamberbeing vacuumized to the extent of 10 mmHg or less; a bellows whichmovably supports one of said electrodes and maintain said vacuum, andmetal shields which surround said electrodes, said one of the electrodeswhich is movable being guided and centered by a guide means, holdingmeans for fixedly mounting the other electrode to said lower lid, andsaid upper lid always being electrically connected with an upper outsideterminal plate irrespective of the position of the movable electrode, aholder for said movable electrode, said guide means having a conductiveportion integral with said upper outside terminal for said movableelectrode and electrically connected with said upper lid and aninsulating portion for centering said movable electrode, the resistancebetween said holder of said movable electrode and said terminal for saidmovable electrode through said guide means being much greater than theresistance through said bellows and said movable electrode.

2. A vacuum circuit breaker comprising at least a pair of electrodesrelatively detachable from each other disposed in a vacuum chamber madeairtight by a surrounding cylinder of insulating material and an upperand lower metal lid attached on both ends thereof, said vacuum chamberbeing vacuumized to the extent of 10 mmHg or less, a bellows whichmovably supports one of said electrodes and maintaining said vacuum; andmetal shields which surround said electrodes, said one of the electrodeswhich is movable being guided and centered by a guide means, holdingmeans for fixedly mounting the other electrode to said lower lid, andsaid upper lid always being electrically connected with an upper outsideterminal plate irrespective of the position of the movable electrode,said vacuum circuit breaker being contained in an airtight tank made ofan insulating material, said tank being filled with an insulatingmedium, the outer surface of said tank ofinsulating material is coveredwith a metal film, said metal film being grounded, the outer surface ofsaid tank having said metal film thereon being spaced from portions ofsaid circuit breaker having an electric potential ap plied thereto.

3. A vacuum circuit breaker comprising a vacuum chamber formed by acylinder of insulating material having an upper metal lid and a lowermetal lid closing the ends thereof, at least a pair of electrode meansrelatively detachable from each other disposed in said chamber, metalshields surrounding said electrodes means, one of said electrode meansbeing fixedly mounted to said lower lid, said other electrode meansbeing movable, a bellows arranged on said upper lid for permittingmovement of said movable electrode means and for maintaining the vacuumwithin said chamber, means for guiding and centering said movableelectrode means, a terminal spaced from said upper lid and electricallyconnected with said movable electrode 3,746,81 1 5 6 means, and meansfor always electrically connecting lows being much greater than theresistance of said said upper lid of said vacuum chamber to saidterminal irrespective of the position of said movable electrode a means,said bellows being electrically connected to said vacuum chamber to sandtermmal' movable electrode means and the resistance of said bel- 5 meanselectrically connecting said upper lid of said

1. A vacuum circuit breaker comprising at least a pair of electrodesrelatively detachable from each other disposed in a vacuum chamber madeairtight by a surrounding cylinder of insulating material and an upperand lower metal lid attached on both ends thereof, said vacuum chamberbeing vacuumized to the extent of 10 4 mmHg or less; a bellows whichmovably supports one of said electrodes and maintain said vacuum, andmetal shields which surround said electrodes, said one of the electrodeswhich is movable being guided and centered by a guide means, holdingmeans for fixedly mounting the other electrode to said lower lid, andsaid upper lid always being electrically connected with an upper outsideterminal plate irrespective of the position of the movable electrode, aholder for said movable electrode, said guide means having a conductiveportion integral with said upper outside terminal for said movableelectrode and electrically connected with said upper lid and aninsulating portion for centering said movable electrode, the resistancebetween said holder of said movable electrode and said terminal for saidmovable electrode through said guide means being much greater than theresistance through said bellows and said movable electrode.
 2. A vacuumcircuit breaker comprising at least a pair of electrodes relativelydetachable from each other disposed in a vacuum chamber made airtight bya surrounding cylinder of insulating material and an upper and lowermetal lid attached on both ends thereof, said vacuum chamber beingvacuumized to the extent of 10 4 mmHg or less, a bellows which movablysupports one of said electrodes and maintaining said vacuum; and metalshields which surround said electrodes, said one of the electrodes whichis movable being guided and centered by a guide means, holding means forfixedly mounting the other electrode to said lower lid, and said upperlid always being electrically connected with an upper outside terminalplate irrespective of the position of the movable electrode, said vacuumcircuit breaker being contained in an airtight tank made of aninsulating material, said tank being filled with an insulating medium,the outer surface of said tank of insulating material is covered with ametal film, said metal film being grounded, the outer surface of saidtank having said metal film thereon being spaced from portions of saidcircuit breaker having an electric potential applied thereto.
 3. Avacuum circuit breaker comprising a vacuum chamber formed by a cylinderof insulating material having an upper metal lid and a lower metal lidclosing the ends thereof, at least a pair of electrode means relativelydetachable from each other disposed in said chamber, metal shieldssurrounding said electrodes means, one of said electrode means beingfixedly mounted to said lower lid, said other electrode means beingmovable, a bellows arranged on said upper lid for permitting movement ofsaid movable electrode means and for maintaining the vacuum within saidchamber, means for guiding and centering said movable electrode means, aterminal spaced from said upper lid and electrically connected with saidmovable electrode means, and means for always electrically connectingsaid upper lid of said vacuum chamber to said terminal irrespective ofthe position of said movable electrode means, said bellows beingelectrically connected to said movable electrode means and theresistance of said bellows being much greater than the resistance ofsaid means electrically connecting said upper lid of said vacuum chamberto said terminal.